The violent and chaotic scene erupted about 12:30 a.m. MDT as a gunman stood at the front of one of the Century 16 theaters at the Aurora Mall where the latest Batman movie "The Dark Knight Rises" was playing, police said.

"Witnesses tell us he released some sort of canister. They heard a hissing sound and some gas emerged and the gunman opened fire," Oates said at a news conference.

Police, ambulances and emergency crews swarmed on the scene after frantic calls started flooding the 911 switchboard, officials said.